Production of gamma isomer of benzene hexachloride



United States Patent Ofiice 2,719,870 Patented Oct. 4, 1955 PRODUCTIONOFGAMMA ISOMER F BENZENE HEXACHLORIDE Philip F. Tryon, Terre Haute,Ind.', assignor to- Commercial Solvents Corporation, Terre Haute, Ind.,a corporation of Maryland No Drawing. Original application December 8,1949, Serial No. 131,898. Divided and this application Decemher 3, 1952,Serial N0. 323,930

9 Claims. (Cl. 260-648) My invention relates to a method for producingsubstantially pure gamma isomer of benzene hexachloride. Morespecifically, it relates to a method of producing substantially puregamma isomer of benzene hexachloride by crystallization from a mixtureof isomers of benzene hexachloride of enhanced gamma isomer content andby the decomposition of benzene hexachloride gamma isomer complexes ashereinafter disclosed. Benzene hexachloride, which is also known as1,2,3,4,- 5,6-hexachlorocyclohexane, is ordinarily produced by reactingbenzene in the liquid phase with chlorine in such a manner as to promotethe addition of the chlorine to benzene. This reaction gives rise to theformation of five isomeric benzene hexachlorides known as the alpha,beta, gamma, delta and epsilon isomers, these isomers being present inthe mixture in varying quantities and possessing different propertiesand utilities. port'ant use of the benzene hexachlorides is asinsecticides, parasiticides, etc. Unfortunately, however, only the gammaisomer is particularly eflective for this purpose and, being present inthe primary reaction product in amounts ranging customarily fromapproximately 10 to of the total reaction mixture, it is'for manypurposes desirable to separate the gamma isomer from the remainingisomers which possess little or no utility for the above purposes. As inthe case of most isomeric compounds a separation of this characterpresents numerous difiiculties and prior to my invention no satisfactorymethod has been available for the separation and recovery ofsubstantially pure gama isomer of benzene hexachloride in a commericallyfeasible manner from its isomers.

In the past the gamma isomer of benzene hexachloride has been producedin several different ways. These processes, however, have beencomercially unfeasible because of their cost and the character of theproducts produced. One of the more important of these processes isdescribed in British Patent 586,439 by Cooke et al. and consists ofdissolving the crude benzene hexachloride in a solvent in which thegamma isomer has a high solubility, and one or all the other isomers alow solubility. This produced a product containing only from 2066% gammaisomer. Another method is reported by Slade in Chemistry and Industry,314 (1945). Slade shows the isolation of the pure gama isomer bytreating the crude benzene hexachloride with methanol, in which thealpha and beta isomers are relatively insoluble, separating the solidproduct, leaving a solution of primarily gama and delta isomers,evaporating this solution and thus obtaining a small amount ofsubstantially pure gamma isomer. The pure gamma isomer of benzenehexachloride is then prepared by recrystallization of the substantiallypure isomer from chloroform.

In carrying out my invention, I start with a mixture of isomers ofbenzene hexachloride containing an enhanced proportion of the gammaisomer. By enhanced proportion of the gamma isomer, I means a mixture ofthe isomers of benzene hexachloride which contains more of the gamaisomer than is normally formed when ben- To date the most im- H a zenehexachloride is produced by the chlorination of benzene, i. e. 10-20%.This mixture of enchanced gamma isomer'content can be prepared in anumber of ways as for example by the method of Cooke et a1. referred toabove. Another and more desirable procedure for preparing the mixture ofisomers of benzene hexachloride, which I use as a starting material incarrying out my invention, consists of first mixing crude benzenehexachloride with about an equal weight of carbon tetrachloride andslurrying the resulting mixture for about one and one-half hours. Theslurry is then filtered and the cake washed with additional carbontetrachloride. The combined filtrate and wash are then steam distilledto remove the carbon tetrachloride. The residue consists of a mixture ofisomers of benzene hexachloride of approximately the followingcomposition: 40-47% gamma isomer, 18-25% alpha isomer, l-3% beta isomer,20-25% delta isomer, and 1 3% epsilon isomer, which forms an oily,crystalline mass. This method of preparing the starting material which Iuse for my invention has, therefore, as will be shown hereafter, theadded advantage of producing at least a 2:1 ratio of gamma to alphaisomer and thus, the starting material prepared in this way can be usedwith any of the solvents which are used in carrying out my invention. Itshould be emphasized, however, that the starting material which I use incarrying out my invention can be prepared in any manner, and is notlimited to the processes shown above.

In carrying out my invention, I first dissolve the oily, crystallinemixture of isomers of benzene hexachloride, containing an enhancedproportion of the gamma isomer, in a solvent in which the solubilityratio of the gamma isomer of benzene hexachloride to the alpha isomer ofbenzene hexachloride is 2 or less, such as for example dioxane,tetrahydropyran, tetrahydrofuran, dioxol'ane, and Z-methyldioxolane.After solution of the mixture of isomers in the solvent, it iscrystallized. The crystals which form are a complex of the gamma isomerof benzene hexachloride and solvent when 1,4-dioXane is used andsubstantially pure gamma isomer of benzene hexachloridewhen the otherabove-mentioned solvents are used.

When dioxane is used as the solvent in carrying out my process, I havefound that the starting material must contain the gamma isomer in atleast a 3:2 ratio to the alpha isomer. As thisratio is decreased theamount of alpha isomer in the product at useful yield levels increasesbeyond an amount wherein the process is practical. When dioxane is usedas the solvent in carrying out my process, a reaction takes place andthe crystalline product formed is bis-(gamma benzene hexachloride)1,4-dioxane (theoretical chlorine 63.53%; determined 63.57%; meltingpoint 7 C.; vapor pressure at 2 C.2 mm Generally the purity of crystalscan be said to be about -100%. Based on the original gamma isomercontent in the mixture of isomers of benzene hexachloride, the yieldwhich can be expected is in the neighborhood of 35-60%. On standingatroom temperature bis '('gamma benzene hexachloride) 1,4-dioxanedecomposes into the gamma isomer of benzene hexachloride and1,4-dioxane. V

The compound bis-(gamma benzene hexachloride) 1,4-dioxane decomposes atroom temperature and pressure-losing 1,4-dioxane, and leaving the gammaisomer of benzene hexachloride. The decomposition can be effected byspreading the crystals of bis-(gamma benzene hexachloride) 1,4-dioxaneto a depthof approximately inch and allowing them to stand at roomtemperature for approximately 24 to 48 hours. The decomposition can beeffected with more rapidity by heating the crys tals and I have foundthat heating at approximately 50 C. for about 4 to 6 hours is suflicientto complete the decomposition.

When tetrahydropyran is used as the solvent in my invention, it isnecessary to use a starting material which contains the gamma isomer inat least a :3 ratio to the alpha isomer. The product formed is acrystalline form of substantially pure gamma isomer of benzenehexachloride.

When tetrahydrofuran is used as the solvent in my invention, it isnecessary to use a starting material which contains the gamma isomer inat least a 3:2 ratio to the alpha isomer. The product formed is acrystalline form of substantially pure gamma isomer of benzenehexachloride.

When dioxolane is used as a solvent in my invention, it is necessary touse a starting material which contains the gamma isomer in at least a2:1 ratio to the alpha isomer. The product formed is a crystalline formof substantially pure gamma isomer of benzene hexachloride.

When 2-methyldioxolane is used as a solvent in my invention, it isnecessary to use a starting material which contains the gamma isomer inat least a 3:2 ratio to the alpha isomer. The product formed is the puregamma isomer of benzene hexachloride and in this case as in the casewhere tetrahydropyran, tetrahydrofuran, and dioxolane are used a complexof the gamma isomer of benzene hexachloride with the solvent is notformed.

Other than the variation of the ratio of gamma isomer to alpha isomer inthe starting material when the different solvents are used and otherthan the fact that decomposition of a complex is necessary in order toobtain the pure gamma isomer of benzene hexachloride when 1,4-dioxane isused, the procedure for carrying out my invention is the same when anyof the above named solvents are used. As already mentioned, the startingmaterial obtained by the procedure shown above is particularlyadvantageous due to the fact that it contains the gamma isomer ofbenzene hexachloride in approximately a 2:1 ratio to alpha isomer. Thisratio of gamma isomer to alpha isomer in the starting material isadequate for use with any of the solvents mentioned herein since thehighest ratio necessary is the 2:1 ratio required when dioxolane isused.

The amount of solvent used to dissolve the mixture of isomers of benzenehexachloride has been found to be at least 0.2 ml. per gram of themixture of isomers. The preferred amount has been found to be from 0.2to 0.8 ml. per gram of the mixture of isomers. The optimum amount for aparticular solvent has been found to depend on the ratio of gamma isomerto alpha isomer in the starting material. As the ratio of gamma isomerof benzene hexachloride to alpha isomer of benzene hexachlorideincreases, the amount of solvent to be used can be adjusted toward thelower limit of the range set out above. For a particular ratio of gammaisomer to alpha isomer in the starting material, the lower limit of therange of amounts of solvent gives some alpha isomer in the product,while the upper limit gives a lower yield.

In isolated cases, I have found that when using an equal amount ofl-butanol or methanol with the crystallization solvent, the yield isincreased, but the results in general show that as a whole there islittle difference in yield when alcohol is used over the use of thecrystallization solvent alone.

By adjusting the temperature to from -25" C., crystallization of theproduct from the solution of the mixture of isomers is facilitated.Slightly better yields are realized by adjusting the temperature towardthe lower limit of the suggested temperature range for crystallization.

The crystalline product in the final mixture can be recovered by anymethod as for example by centrifuging the product mixture, and washingthe crystals while still in the centrifuge with butanol. The crystalsare then removed from the centrifuge and dried in order to obtain thegamma isomer of benzene hexachloride.

The following examples are offered to show specific embodiments of myinvention, but are not intended to limit the scope of the invention tothe examples as shown. In each experiment, unless otherwise stated, theprocedure used consisted of first dissolving the mixture of isomers,containing an enhanced proportion of gamma isomer, in

the crystallization solvent, mixed with alcohol, if desired.

300 grams of a mixture of isomers of benzene hexachloride containing 141grams of the gamma isomer, 60 grams of the alpha isomer, 72 grams of thedelta isomer, and 5.7 grams of the epsilon isomer were dissolved in 100ml. of dioxane (0.33 ml. of dioxane per gram of mixture of isomers).Upon cooling to approximately 15 C. crystals formed. (Analysis: Cl,theory, 63.53; found, 63.57. Melting point, C.). The latter werecentrifuged, washed, and left in air for 24 hours. grams of 99% puregamma isomer (M. P. l08-111) were obtained. This amounted to a 60% yieldof gamma isomer on the basis of the gamma isomer content of the abovemixture of isomers.

Example II 280 grams of a mixture of isomers of benzene hexachloridecontaining 123 grams of the gamma isomer, 50 grams of the alpha isomer,78 grams of the delta isomer, and 15 grams of the epsilon isomer weredissolved in 56 ml. of dioxane (0.2 ml. of dioxane per gram of mixtureof isomers). After crystallization, washing, and leaving in air, 83grams of a product consisting of 83% gamma isomer (M. P. l01108) wasobtained. This amounted to a yield of 56% on the basis of the gammaisomer content of the above mixture of isomers.

Example III 280 grams of a mixture of isomers of benzene hexachloridecontaining 126 grams of the gamma isomer, 58 grams of the alpha isomer,78 grams of the delta isomer, and 8.4 grams of the epsilon isomer weredissolved in 112 ml. of dioxane (0.4 ml. of dioxane per gram of mix:ture of isomers). After crystallization, washing, and leaving in air, 68grams of a product consisting of 98% gamma isomer (M. P. 110-1l3) wasobtained. This amounted to a yield of 53% on the basis of the gammaisomer content of the above mixture of isomers.

Exa mple IV 280 grams of a mixture of isomers of benzene hexachloridecontaining 123 grams of gamma isomer, 50 grams of alpha isomer, 78 gramsof the delta isomer, and 15 grams of the epsilon isomer were dissolvedin 224 ml. of dioxane (0.8 ml. of dioxane per gram of mixture ofisomers). After crystallization, washing, and leaving in air, 48 gramsof a product consisting of gamma isomer (M. P. 111114) was obtained.This amounted to a yield of 37% on the basis of the gamma isomer contentof the above-mentioned mixture of isomers.

Example V 300 grams of a mixture of isomers of benzene hexachloridecontaining 141 grams of the gamma isomer, 60 grams of the alpha isomer,78 grams of the delta isomer, and 5.1 grams of the epsilon isomer weredissolved in ml. of tetrahydrofuran (0.33 ml. of tetrahydrofuran pergram of mixture of isomers). After crystallization and drying 30 gramsof a product consisting of 99% gamma isomer (M. P. 112 114 was obtained.This amounted to a yield of 21% on the basis of the gamma isomer contentof the above mixture of isomers.

Example VI 300 grams of a mixture of isomers of benzene hexachloridecontaining 141 grams of the gamma isomer, 60 grams of the alpha isomer,78 grams of the delta isomer, and 5.1 grams of the epsilon isomer weredissolved in 100 ml. of tetrahydropyran (0.33 ml. of tetrahydropyran pergram of mixture of isomers). After crystallization and drying, 51 gramsof a product consisting of 99% gamma isomer (M. P. ll1-1l4) wasobtained. This amounted to a yield of 36% on the basis of the gammaisomer content of the above mixture of isomers.

Example VII 300 grams of a mixture of isomers of benzene hexachloridecontaining 141 grams of the gamma isomer, 60 grams of the alpha isomer,78 grams of the delta isomer, and 5.1 grams of the epsilon isomer weredissolved in 100 ml. of dioxolane (0.33 ml. of dioxolane per gram of themixture of isomers). After crystallization and drying, a productconsisting of 97% gamma isomer (M. P. ll-1l3) was obtained.

Example VIII 300 grams of a mixture of isomers of benzene hexachloridecontaining 141 grams of the gamma isomer and 60 grams of the alphaisomer were dissolved in 100 m1. of Z-methyldoxolane (0.33 ml. ofZ-methyldioxolane per gram of the mixture of isomers). Aftercrystallization and drying, 83 grams of a product consisting of 90%gamma isomer (M. P. 104106) was obtained. This amounted to a yield of53% on the basis of the gamma isomer content of the above mixture ofisomers.

While the foregoing examples illustrate embodiments of my invention, itis to be understood that departure may be made therefrom within thescope of the specification and claims. In general, it may be said thatany modification or equivalents that would ordinarily occur to thoseskilled in the art are to be considered as lying within the scope of myinvention.

This application is a division of my pending application Serial No.131,898 filed December 8, 1949, now U. S. Patent No. 2,673,857.

In accordance with the foregoing specification, I claim as my invention:

1. In a process for obtaining substantially pure gamma isomer of benzenehexachloride, the steps which comprise dissolving in a solvent selectedfrom the group consisting of tetrahydropyran, tetrahydrofuran,dioxolane, and 2-methyldioxolane, a mixture of benzene hexachlorideisomers containing the gamma isomer in a greater than 2:1 ratio to thealpha isomer, and cooling said resulting solution to effectcrystallization of the substantially pure gamma isomer of benzenehexachloride.

2. In a process for obtaining substantially pure gamma isomer of benzenehexachloride, the steps which comprise dissolving in tetrahydrofuran amixture of benzene hexachloride isomers containing the gamma isomer. ina greater than 2:1 ratio to the alpha isomer, cooling said resultingsolution to efiect crystallization of substantially pure gamma isomer ofbenzene hexachloride.

3. In a process for obtaining substantially pure gamma isomer of benzenehexachloride, the steps which comprise dissolving a mixture of benzenehexachloride isomers containing the gamma isomer in a greater than 2:1ratio to the alpha isomer in at least 0.2 ml. of tetrahydrofuran pergram of mixture of benzene hexachloride isomers, adjusting thetemperature of the resulting solution to from 15 to 25 C. and therebycrystallizing out of the solution substantially pure gamma isomer ofbenzene hexachloride.

4. In a process for obtaining substantially pure gamma isomer of benzenehexachloride, the steps which comprise dissolving in tetrahydropyran amixture of benzene hexachloride isomers containing the gamma isomer in agreater than 2:1 ratio to the alpha isomer, cooling said resultingsolution to effect crystallization of substantially pure gamma isomer ofbenzene hexachloride.

5. In a process for obtaining substantially pure gamma isomer of benzenehexachloride, the steps which comprise dissolving a mixture of benzenehexachloride isomers containing the gamma isomer in a greater than 2:1ratio to the alpha isomer in at least 0.2 ml. of tetrahydropyran er gramof mixture of benzene hexachloride isomers, adjusting the temperature ofthe resulting solution to from 15 to 25 C. and thereby crystallizing outof the solution substantially pure gamma isomer of benzene hexachloride.

6. In a process for obtaining substantially pure gamma isomer of benzenehexachloride, the steps which comprise dissolving in dioxolane a mixtureof benzene hexachloride isomers containing the gamma isomer in a greaterthan 2:1 ratio to the alpha isomer, cooling said resulting solution toeffect crystallization of substantially pure gamma isomer of benzenehexachloride.

7. In a process for obtaining substantially pure gamma isomer of benzenehexachloride, the steps which comprise dissolving a mixture of benzenehexachloride isomers containing the gamma isomer in a greater than 2:1ratio to the alpha isomer in at least 0.2 ml. of dioxolane per gram ofmixture of benzene hexachloride isomers, adjusting the temperature ofthe resulting solution to from 15 to 25 C. and thereby crystallizing outof the solution substantially pure gamma isomer of benzene hexachloride.

8. 'In a process for obtaining substantially pure gamma isomer ofbenzene hexachloride, the steps which com- 7 prise dissolving in2-methyldioxolane a mixture of benzene hexachloride isomers containingthe gamma isomer in a greater than 2:1 ratio to the alpha isomer,cooling said resulting solution to eifect crystallization ofsubstantially pure gamma isomer of benzene hexachloride.

9. In a process for obtaining substantially pure gamma isomer of benzenehexachloride, the steps which comprise dissolving a mixture of benzenehexachloride isomers containing the gamma isomer in a greater than 2:1ratio to the alpha isomer in at least 0.2 ml. of 2-methyldioxolane pergram of mixture of benzene hexachloride isomers, adjusting thetemperature of the resulting solution to from 15 to 25 C. and therebycrystallizing out of the solution substantially pure gamma isomer ofbenzene hexachloride.

2,438,900 Cooke et a1. Apr. 6, 1948

1. IN A PROCESS FOR OBTAINING SUBSTANTIALLY PURE GAMMA ISOMER OF BENZENEHEXACHLORIDE, THE STEPS WHCIH COMPRISES DISSOLVING IN A SOLVENT SELECTEDFROM THE GROUP CONSISTING OF TETRAHYDROPYRAN, TETRAHYDRROFURAN,DIOXOLANE, AND 2-METHYLDIOXOLANE, A MIXTURE OF BENZENE HEXACHLORIDEISOMERS CONTAINING THE GAMMA ISOMER IN A GREATER THAN 2:1 RATIO TO THEALPHA ISOMER, AND COOLING SAID RESULTING SOLUTION TO EFFECTCRYSTALLIZATION OF THE SUBSTANTIALLY PURE GAMMA ISOMER OF BENZENEHEXACHLORIDE.